God Rays through window pane: Cycles
Use a cuboid to surround the scene, and use a volume scatter node as volume. Nothing shoud be connected to the surface socket.
The default value of 1 for volume scatter is way too dense for practical use, so use a much smaller value.

Add a point light and make it very small (in this example is 0m) and very, very, very bright. The smaller the light, the more defined the shadows will be.

If you are using a glass material for the windows, you have to modify it so that it let's direct light go through it.

For more info on the glass shader read:
How to illuminate the dark areas behind glass in cycles
As for the noise... use a lot of samples.